Investigation on the Influence of Basic Workability Parameters on the Mechanical Behavior and Gradient Structure of the Filling Layer

Self-compacting concrete (SCC) has been extensively utilized in the construction of high-speed railways in China. However, fresh SCC’s high paste volume and low coarse aggregate content inevitably increase its segregation tendency, compromising the stability of SCC mixtures. This study aims to examine the impact of slump flow (SF) and T 500 on the mechanical properties and gradient structure of the filling layer. (In the assessment of the slump of a concrete mixture using a slump cone, the time (in seconds) is measured from the moment the cone is lifted until the slump expansion achieves a measurement of 500 mm.) Additionally, the gradient structure of the filling layer is analyzed using microhardness testing and backscattered electron imaging coupled with image analysis. The findings indicates that the compressive strength of the filling layer exhibits a gradient variation along the filling direction, with higher compressive strength observed centrally around the filling hole in the transverse direction. This gradient variation can be enhanced by reducing SF or increasing T 500 , whereas the filling time shows minimal impact on the homogeneity of the filling layer. The segregation rate of the filling layer exhibits a gradient increase along the filling direction. There is a negative correlation between SF and both the segregation rate and the paste/mortar layer thickness of the filling layer. T 500 significantly impacts the segregation rate and paste/mortar layer thickness; specifically, both the segregation rate and the thickness of the paste/mortar layer increase with higher T 500 . Enhancing the gradient structure of the filling layer can be achieved by regulating the workability of SCC mixtures.